The present invention relates to a method for manufacturing a liquid crystal display. More particularly, the present invention relates to a method for manufacturing a liquid crystal display having a thin film transistor as an active device, by which it is possible to reduce the number of the photolithography processes.
The liquid crystal display (LCD) is currently the most widely used flat-panel display device. Other devices being developed and rapidly becoming popular include the plasma display panel (PDP), the electro luminescence (EL) device, the field emission display (FED), and the reflex deformable mirror device (DMD), which controls the movement of a mirror.
The LCD uses an optical characteristic of liquid crystal molecules in which the arrangement thereof changes according to an electrical field and a semiconductor technology which forms minute patterns. A thin film transistor LCD (“TFT-LCD”), which uses the thin film transistor as the active device, has various advantages over other LCDs. These advantages include low power consumption, low drive voltage, a thinness, and lightness of weight, among others.
Since the thin film transistor (“TFT”) is significantly thinner than a conventional transistor, the process of manufacturing a TFT is complicated, resulting in low productivity and high manufacturing costs. In particular, since a mask is used in every step for manufacturing a TFT, at least seven masks are required. Therefore, various methods for increasing productivity of the TFT and lowering the manufacturing costs have been studied. In particular, a method for reducing the number of the masks used during the manufacturing process has been widely researched.
FIGS. 1 to 5 are sectional views for explaining a conventional method for manufacturing an LCD, as disclosed in U.S. Pat. No. 5,054,887.
In the drawings, reference characters “A” and “B” denote a TFT area and a pad area, respectively. Referring to FIG. 1, after forming a first metal film by depositing pure Al on a transparent substrate 2, gate patterns 4 and 4a are formed out of the first metal film by performing a first photolithography on the first metal film. The gate patterns are then used as a gate electrode 4 in the TFT area and as a gate pad 4a in the pad area.
As shown in FIG. 2, after forming by general photolithography a second photoresist pattern (not shown) that covers a portion of the pad area, an anodized film 6 is formed by oxidizing the first metal film using the photoresist pattern as an anti-oxidation film. The anodized film 6 is then formed on the entire surface of the gate electrode 4 formed in the TFT area, and on a portion of the gate pad 4a in the pad area.
Referring to FIG. 3, an insulating film 8 is formed by depositing a layer such as a nitride film over the anodized film 6. A semiconductor film is then formed by subsequently depositing an amorphous silicon film 10 and an amorphous silicon film 12 doped with impurities on the entire surface of the substrate 2 on which the insulating film 8 is formed. A semiconductor film pattern 10 and 12 to be used as an active portion is then formed in the TFT area by performing a third photolithography on the semiconductor film.
As shown in FIG. 4, a fourth photoresist pattern (not shown) is then formed that exposes a portion of the gate pad 4a formed in the pad area by performing a fourth photolithography on the entire surface of the substrate 2 on which the semiconductor film pattern is formed. Then, a contact hole is then formed in the insulating film 8, which contact hole exposes a portion of the gate pad 4a. The contact hole is formed by etching the insulating film 8 using the fourth photoresist pattern as a mask. A source electrode 14a and a drain electrode 14b are then formed in the TFT area by depositing a chromium (“Cr”) film on the entire surface of the substrate having the contact hole and performing a fifth photolithography on the Cr film. In the pad area, a pad electrode 14c connected to the gate pad 4a through the contact hole is formed. At this time, the impurity doped-amorphous silicon film 12 on the upper portion of the gate electrode 4 formed in the TFT area during the photolithography process is partially etched, thus exposing a portion of the amorphous silicon film 10.
Referring to FIG. 5, a protection film 16 is then formed by depositing an oxide film over the entire surface of the substrate 2 on which the source electrode 14a, the drain electrode 14b and the pad electrode 14c are formed. Then, contact holes are formed that expose a portion of the drain electrode 14b of the TFT area and a portion of the pad electrode 14c of the pad area. The contact holes are formed by performing a sixth photolithography on the protection film 16.
Subsequently, pixel electrodes 18 and 18a are formed by depositing indium tin oxide (“ITO”), a transparent conductive material, over the entire surface of the substrate, including the contact hole, and performing a seventh photolithography process on the resultant ITO film. As a result of this seventh lithography, the drain electrode 14b and the pixel electrode 18 are connected in the TFT area, and the pad electrode 14c and the pixel electrode 18a are connected in the pad area.
According to the conventional method for manufacturing the LCD, pure aluminum (“Al”) is used as the gate electrode material to lower the resistance of a gate line. An anodizing process is therefore required to prevent a hillock caused by the Al. This additional anodizing step complicates the manufacturing process, reduces productivity, and increases manufacturing costs.